Production of alloy materials



July 7, 1964 B. c. com 3,140,172

PRODUCTION OF ALLOY MATERIALS Filed June 30, 1961 f/5 TW/sJ?/////`/`///////// ////s L\ i7\\ \\\\\\\\1 f3 *s'/ F'G'5'"1\\\\\\\\\\\\\\\\\ F9721#-j SW GDM, L

United States Patent O 3,140,172 PRODUCTION F ALLOY MATERIALS Brian C.Coad, Attleboro, Mass., assigner to Texas Instruments Incorporated,Dallas, Tex., a corporation of Delaware Filed .lune 30, 1961, Ser. N123,934 6 Claims. (Cl. 7S--122) This invention relates to an improvedmethod for the production of alloy materials, and to the fabrication ofimproved products made therefrom, and more particularly to alloys ofiron and aluminum.

Among the several objects of the invention may be noted the provision ofan improved, simpler and less costly method for obtaining alloys,particularly those such as iron and aluminum, which may be quite brittlebecause, for example, of a high aluminum content, the compositions ofwhich by means of the invention are more precisely controllable thanheretofore; the provision of such a method which avoids need for complexmelting techniques; the provision of a method for obtaining productsincorporating iron-aluminum alloys in bonded form which avoids formerdifficulties encountered in attempts to coldwork such iron-aluminumbrittle alloys in the required bonding operations; and the provision ofiron-aluminum alloy products which have desirable physicalcharacteristics as required for various uses. Other objects and featureswill be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations ofelements, steps and sequence of steps, features of construction andmanipulation, and arrangements of parts which will be exemplified in theproducts and methods hereinafter described, and the scope of which willbe indicated in the following claims.

In the accompanying drawings, in which several of various possibleembodiments of the invention are illustrated,

FIG. 1 is a diagrammatic cross section of a typical bonded compositesheet of aluminum and iron useful for carrying out the invention;

FIG. 2 is a View similar to FIG. 1, illustrating a conversion of theFIG. l sheet after a first heating step;

FIG. 3 is a View similar to FIGS. 1 and 2, showing a final conversion ofthe FIG. 2 sheet into a finished product after a second heating step;

FIG. 4 is a diagrammatic sectional view of a starting composite sheetfor producing magnetizable elements such as used for transformers andthe like;

FIG. 5 is a view similar to FIG. 4, illustrating a conversion of theFIG. 4 sheet after a lirst heating step; and

FIG. 6 is a View similar to FIGS. 4 and 5, showing a nal conversion ofthe FIG. 5 sheet into a finished product after a second heating step.

Corresponding reference characters indicate corresponding partsthroughout the several views of the drawings.

While the invention has certain characteristics broadly applicable tovarious metals, it is particularly useful in the iield of iron-aluminumalloys. Iron-aluminum alloy materials are characterized by goodoxidation resistance, high electrical resistance and low density, ascompared with most other iron alloys. They also have good socalled softmagnetic properties, meaning that they are easily magnetized under lowcoercive forces and that they spontaneously and rapidly demagnetizethemselves. In the past, however, problems have been encountered inmaking such alloys by conventional melting techniques because of thedisparity in the melting temperatures of the components. This made itdiflicult to achieve precise control of the compositions. Anotherdiiculty manifested itself with such alloys when they containedsubstantial amounts of aluminum in that then these alloys ICC becamemore diiiicult to cold-work in view of their increased brittleness.According to the present invention, solid-state type alloying techniquesare employed in a manner to obtain closer control of compositions and soas to avoid the above-mentioned cold-working difficulties in making upcertain types of products. This is in addition to the ability to obtainat lower cost a more closely controlled composition of the alloy.

Briey, in its iron-aluminum alloy application, the present invention inone form is carried out by bonding one or more sheets of aluminum to aniron base sheet, then reducing the resulting composite material thusobtained to finished size by rolling or otherwise, after which thecomposite is heat-treated a first time to produce intermetalliccompounds of iron and aluminum on the iron base. Thereafter, thecomposite is heat-treated a second time so as to bring about an alloyingof the intermetallic compound with the iron, thus producing a solidsolution of aluminum and iron. This constitutes the desired alloy. Theinvention may be carried out to produce the desired alloy insingle-sheet form or to produce it in attachment with other sheets, suchas magnetic alloy sheets used for transformer cores or the like, inwhich cases a composite material results, the brittle iron-aluminumcomponents requiring no complex or cumbersome working to get them bondedto the core sheets. The invention may also be carried out in stepsemploying powder forms of certain components, as will be described inmore detail below.

Referring now more particularly to FIG. 1 of the drawings, there isshown at numeral 1 an iron base sheet which may be composed of a lowcarbon steel, for example, 1010 steel. To this has been metallurgicallybonded two cladding sheets 3 of aluminum. Appropriate cladding means andmethods are, for example but Without limitation, disclosed in UnitedStates Patents 2,691,815 and 2,753,623. Solid-phase bonding, such asshown in these patents, is employed in carrying out the inventionbecause no extraneous material is involved at the bond, other thanintermetallic compounds of the metals which `are preliminarily bonded,such metals being those which ultimately make up the desired alloy. Thebonded sheet is rolled down to a total thickness of, for example, .005inch, which is to say that the sheet may have been rolled down from apreviously bonded ironaluminum combination of greater thicknesses of itsvarious layers. The thickness ratio of aluminum-iron-aluminum as rolleddown is, for example, 10-80-10. This provides approximately 8% ofaluminum by weight in the composite sheet shown in FIG. 1, according tothis example.

The .O05 inch composite sheet example thus described and illustrated inFIG. 1 is subjected to a first heating step by heating in air for anhour or so to a temperature in the range from 1,000 F. to 1,500 F. Sincethe melting point of aluminum is approximately 1,200 F., thistemperature range covers cases in which the aluminum does not meltduring the first heating step, and cases wherein it does so. It has beenfound that even when the temperature of the iirst heating step exceedsthe melting point of aluminum that little or no difliculty isencountered with run-off of the aluminum during this first heating step.While I do not wish to be bound by any theories, it is believed thatthis phenomenon may at least in part be due to the thinness of thealuminum layer, which permits surface ltension to preponderate over anytendency to run-olf, and due in part to the presence of an oxide lm onthe aluminum cladding which also helps to prevent run-off.

FIG. 2 shows the result of the iirst heating step above described whichis the conversion of the aluminum layers 3 of FIG. 1 into layers 5 and7, shown in FIG. 2. These 3 are constituted'by intermetallic compoundsof iron and aluminum, such as, for example, Fe3Al5 and others. In FIG. 2the base is numbered 1.

Next a diffusion or homogenizing step is employed wherein the productillustrated in FIG. 2 is transferred to a controlled-atmosphere lfurnacehaving, for example, an inert or nonoxidizing atmosphere such as argonto prevent further oxidation 'such as may have occurred in the firstheating step. This furnace is operated at or above the melting point ofthe intermetallic compounds constituting lthe cladding sheets 5 yand 7of FIG. 2. Thus, the approximate melting point of the ironaluminumintermetallic compound, for example, Fe3Al5, is 2,120 F. Therefore, asatisfactory operating temperature for the controlled-atmosphere furnaceis 2,300 F. This is below the melting point of iron, which melts atapproximately 2,800 F. Again, the layers of the intermetallio compoundsdo not tend to run off. Heating is continued at the selected temperatureof 2,300 F., for example, for approximately four hours. The exactmaximum temperature that may be carried in the controlled-atmospherefurnace depends somewhat upon the percentage of the ratio of aluminum toiron used, because the melting point of iron-aluminum alloy produced,varies somewhat with the percentage of aluminum therein. It is alsointended -not to exceed at any stage the melting point of the iron basesheet 1 or 1. Thus the desirable temperature range of operation of thisfurnace may be between 2,120 F. and the melting point of iron, asinfluenced by the amount of aluminum that it may have in it as thisheating step proceeds. However, 2,300 F. is a satisfactory temperature.After the four-hour 2,300 F. heat treatment, the layers 1, 5 and 7 ofFIG. 2 become converted to a homogeneous solid solution alloy of ironand aluminum, being a true alloy of these components. This isillustrated at numeral 9 in FIG. 3.

An advantage of this method of making iron-aluminum alloys lies in thefact that an unalloyed composite such as shown in FIG. 1 can be annealedand readily formed, since no substantial brittle stage has been reachedwhich would complicate such working or render the material unworkable.This is subsequently alloyed as described in connection with FIGS. 2 and3 by the simple heat treatments described herein. This postpones thebrittle condition until any desired working has been completed.Iron-aluminum alloys as made by the former all-liquidphase method reachthe brittle condition before working is possible, so that any workingstep required becomes costly and difficult and in some cases impossible.Former methods also have resulted in alloys and problems generallycharacterized by lack of homogeneity in the alloy, and by poor ductilityand formability, all of which problems are obviated or at leastminimized by means of the present invention.

The iron-aluminum ratio selected for the clad material of FIG. l is suchas to obtain the percentage of aluminum desired inthe finished alloy. Insome instances the first heating step described in connection withconvert-ing from the FIG. l formation to the FIG. 2 formation may beomitted; but it is preferred that it be employed because it is believedthat greater uniformity of composition and cross section may be achievedwith the two-step process.

It should be understood that both the first and second heating stepsdescribed above may, in some cases, conveniently be carried out in acontrolled, non-oxidizing atmosphere-furnace or in the air, if desired.

Other alternative examples of the above method are as follows:

As first and second alternatives, 1010 steel may be clad with 2Saluminum in 14-72-14 and 17-66-17 thickness ratios, to produceapproximately 12% aluminum and 15% aluminum by weight of iron-aluminumalloys, respectively. The clad composites have been rolled to CII 4 .005inch at the time that said ratios are obtained. The composites are thenheated while loosely coiled for one hour at l,500 F. in air to formiron-aluminum compounds including Fe3Al5; then four hours at 2,300 F. inargon, to produce the 12% and 15 alloys by diiusion, as above set forth.

As a third alternative, a starting layer may be employed consisting ofbonded 2S aluminum, 310 stainless steel and 2S aluminum in a 5-90-5thickness ratio, having a total thickness of .005 inch. This is firstheated for one-half hour at l,200 F. to form the desired intermetalliccompounds; then heated for diffusion for two hours at 2,300 F. to makethe alloy. In this case, both heating steps are carried out in air. Theresulting aluminum content of the alloy is approximately 3.5%.

In FIGS. 4-6 is illustrated anapplication of the invention to theproduction of magnetic or magnetizable core, armature, field and likemembers for transformers, motors, generators and the like. In FIG. 4,numeral 11 illustrates a base sheet of, for example, any conventionalmagnetic alloy such as is now used for making transformer cores. Anexample of such an alloy is silicon iron. Clad to the magnetic alloysheet 11 are sheets 13 of iron, and clad to these iron sheets are sheets15 of aluminum. The iron of sheets 13 may be in the form of a low carbonsteel such as 1010 steel and preferably in the form of substantiallypure iron.

The thickness of the magnetic alloy base material 11 is arbitrary.Assume it to be units. Then the ratio of thicknesses of the layers 15,13, 11, 13, 15 may for example be 10440-100440-10. The over-allthickness of the FIG. 4 assembly will be that ordinarily desired for useof the final product such as, for example, a sheet useful as transformercore material. This thickness may for example be from .012 inch formedium size transformers.

The bonded assembly thus formed (FIG. 4) is first heated in air for onehour to a temperature in the range of from l,000 F. to 1,500 F. Thisproduces an intermediate material illustrated in FIG. 5, wherein themagnetic alloy base 11 carries on it layers of iron 13', and on theselayers 13', layers 17 of intermetallic compounds such as Fe3Al5.` Thenthe product of FIG.l 5 is subjected to the second heat treatment in aprotective or nonoxidizing atmosphere at 2,300c F. for approximatelyfour hours, with the result shown in FIG. 6, wherein the magnetic alloycore material 11 is clad with layers 19 of iron-aluminum alloy. The FIG.6 material then consists of the usual magnetic core material fortransformers, faced with a bonded high-resistance iron-aluminum alloy19. The interleaved iron-aluminum alloy sheets, having a highresistance, reduce eddy-current losses in the electrical devicesemploying them in laminated form. It should be understood that thetemperature and time for `the second heating step are so selected inaccordance with the thickness of the iron layers 13', 13 so as tosubstantially avoid diffusion or penetration of the aluminum into thesilicon iron layer 11.

The invention may also be carried out with finely divided or comminutedstarting materials instead of the solid sheet materials as in FIGS. land 4. Thus, for example, finely divided aluminum and finely dividediron in a 50-50 ratio by weight are mixed thoroughly. The degree ofcomminution of the components is` not critical. The particles may rangein size from small pellets, chips or the like, to powder. The mixedcomponents are then compacted into appropriate form by rolling, pressingor the like. Next the compacted form is heat-treated for example for onehour at l,300 F. in an atmosphere, for example, of cracked ammonia, tosinter and produce solidified intermetallic compounds. The resultingintermediate product includes, for example, Fe3Al5. The compactedintermediate product is broken up by ball milling, again to formcomminuted particles, which at this time becomes a finely divided formof the intermetallic compound. This is hereinafter referred to as powderA.

Next, finely divided iron is mixed with, for example, 24% by weight ofpowder A, to provide, if so desired, a final iron-aluminum alloycontaining approximately 12% of aluminum by weight. A finaliron-aluminum alloy having approximately 16% aluminum by weight would beobtained by mixing powdered iron with 32% by weight of powder A. Ineither case, the mixture of iron and powder A is compacted by rolling,pressing or the like to form a sheet, strip, pellet, shape or part offinal desired configuration which is thereafter heat-treated for examplefor three hours at 2,250@ F. This results in a homogeneous iron-aluminumalloy containing approximately 12% or 16% aluminum, as the case may be.It will be understood that, by employing powder proportions other thanthose described above, other proportions of aluminum may be obtained inthe final iron-aluminum alloy.

If desired, one of the mixtures of finely divided iron and 24% (forexample) by weight of powder A may, during compaction, be rolled ontoand bonded to a suitable base material such as the magnetic alloy sheetabove mentioned. Then upon applying the alloying heating step to thecompacted mixture of finely divided iron and powder A as rolled on thebase material, the mixture will be converted into the finaliron-aluminum alloy, the alloy bonded to the base material.

ln view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made inthe above products and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

I claim:

1. The method of producing an alloy, comprising solidphase bonding androlling to a small thickness, on the order of a few thousandths of aninch, layers of all of the constituents required in individualthicknesses adapted to supply the correct proportions thereof in thedesired alloy, heating the bonded layers to form an intermediatemultilayer sheet in which substantially all of one constituent and someof the other are converted to at least one intermetallic compound in atleast one bonded layer, some of the constituent material remaining asanother bonded layer, and then heating the layers in the multi-layerstate at a temperature adapted to convert them from their multilayerstate to the desired alloy in a single-layer state.

2. The method according to claim 1, wherein one of said layers comprisesaluminum and the other comprises iron, the total thickness of thealuminum and iron layers being selected to be on the order of a fewthousandths of an inch.

3. The method of producing magnetizable core material comprisingcladding by solid-phase bonding on a magnetizable alloy sheet at leasttwo sheets having multi-layer constituents of different metals, saidsheets being also solid-phase bonded, each of the constituent layersbeing of small thicknesses on the order of a few thousandths of an inchand in a ratio adapted to supply the correct proportions thereof indesired alloy cladding, heating the bonded layers to form anintermediate multi-layer sheet in which substantially all of oneconstituent and some of the other are converted to at least oneintermetallic compound, and then heating all of the layers to convertthem to the desired alloy.

4. The method of producing magnetic core material comprising solid-phasebonding to a first sheet of a magnetic alloy second and third sheets ofsolid-phase bonded layers of aluminum and iron, said second and thirdlayers being of a total thickness on the order of a few thousandths ofan inch, the respective thicknesses of said second and third layersadapted to supply the correct proportions thereof in a desired alloyfacing on the first layer, heating the three bonded layers to form anintermediate multiply sheet in which the first layer is preserved andsubstantially all of the third layer and some of the second layer areconverted to at least one intermetallic compound, and then heating allof the layers at a temperature sufficient to convert the second andthird layers to form the desired alloy in unit-layer form on the firstlayer.

5. The method of producing magnetizable clad core material in sheet formcomprising cladding by solid-phase bonding on each of opposite sides ofa magnetizable alloy sheet one double-layer sheet, each sheet beingcomposed of different constituent metals, each of said sheets being ofsmall thickness on the order of a few thousandths of an inch, thecomponent layers of each sheet being in thicknesses adapted to supplythe correct proportions thereof in desired alloy cladding, heating allof the bonded layers to form an intermediate multi-layer sheet on eachside of the magnetizable alloy sheet in which substantially all of oneconstituent and some of the other are converted to at least oneintermetallic compound, some of the constituent material remaining asanother layer,I and then heating all of the layers to convert them tothe desired alloy cladding on each side ofthe core material.

6. The method of producing an alloy comprising mixing portions ofdifferent finely divided particles of first and second metals, pressingthe mixed portions to compact them, heat-treating said compactedportions at a sintering emperature adapted to form a solid including inits constituent materials an intermetallic compound, finely dividingsaid sintered solid into finely divided material, mixing the last-namedfinely divided material with an additional amount of one of said finelydivided metals to form a mixture of particles to supply all of theconstituents required in a proper proportion of the desired alloy,pressing the particles of said last-named mixture by rolling themagainst a sheet of metaliic base material, and heat-treating said sheetof base material with the mixture pressed thereon to bond said mixtureto the base material and to convert the mixture into the desired alloy.

References Cited in the file of this patent UNITED STATES PATENTS1,223,322 Gebauer Apr. 17, 1917 2,845,365 Harris July 29, 1958 FOREIGNPATENTS 216,484 Great Britain Oct. 30, 1924 716,604 Great Britain Oct.13, 1954

1. THE METHOD OF PRODUCING AN ALLOY, CMPRISING SOLIDPHASE BONDING ANDROLLING TO A SMALL THICKNESS, ON THE ORDER OF A FEW THOUSANDTHS OF ANINCH, LAYERS OF ALL OF THE CONSTITUENTS REQUIRED IN INDIVIDUALTHICKNESSES ADPATED TO SUPPLY THE CORRECT PROPORTIONS THEREOF IN THEDESIRED ALLOY, HEATING THE BONDED LAYERS TO FORM AN INTERMEDIATEMULTILAYER SHEET IN WHICH SUBSTANTIALLY ALL OF ONE CONSTITUENT AND SOMEOF THE OTHER ARE CONVERTED TO AT LEAST ONE INTERMETALLIC COMPOUND IN ATLEAST ONE BONDED LAYER, SOME OF THE CONSTITUENT MATERIAL REMAINING ASANOTHER BONDED LAYER, AND THEN HEATING THE LAYERS IN THE MULTI-LAYERSTATE AT A TEMPERATURE ADAPTED TO CONVERT THEM FROM THEIR MULTILAYERSTATE TO THE DESIRED ALLOY IN A SINGLE-LAYER STATE.